| Station Code | Station Name | Number of Trains |
|---|---|---|
| OBAC | Obra-a-cabin | 0 |
| OBM | Obalapuram | 4 |
| OBR | Obra dam | 20 |
| OBVP | Obulavaripalli | 10 |
| OCH | Obhaniya chache | 2 |
| OCR | Ochira | 14 |
| OD | Od | 13 |
| ODB | Oodlabari | 8 |
| ODC | Oddam hatram | 8 |
| ODG | Obaidulla ganj | 12 |
| ODHA | Odha | 6 |
| ODM | Ondagram | 27 |
| ODOA | Osmanabad o.a. | 0 |
| ODUR | Odur | 8 |
| OEA | Odela | 14 |
| OEL | Oel | 11 |
| OFB | Ordnance factory | 0 |
| OGL | Ongole | 157 |
| OGM | Oorgaum | 20 |
| OHAN | Ohan | 1 |
| OKA | Okhla | 51 |
| OKAC | Okhla bypass b cabin station | 0 |
| OKD | Okha madhi | 3 |
| OKHA | Okha | 34 |
| OKL | Ottakkal | 0 |
| OKO | Okha | 0 |
| OLA | Olakur | 4 |
| OLAF | Olakur | 0 |
| OLP | Olapur | 10 |
| OLR | Ollur | 11 |
| OM | Omkareshwar rd | 12 |
| OMB | Oombermali | 34 |
| OML | Omalur | 10 |
| OMLF | Old malda | 16 |
| ON | Unnao jn | 99 |
| OND | Aunlajori jn | 4 |
| ONR | Coonoor | 8 |
| OPL | Uppal | 12 |
| OPN | Onnupuram halt station | 0 |
| ORAI | Orai | 55 |
| ORC | Orchha | 8 |
| ORD | Orcha dham | 0 |
| ORDF | Ordi | 0 |
| ORDI | Ordi | 4 |
| ORE | Ore halt | 0 |
| OREH | Ore halt | 9 |
| ORGA | Orga | 6 |
| ORH | Oddarahalli | 3 |
| ORKI | Orki | 6 |
| ORR | Orr | 14 |
| ORW | Orwara | 6 |
| OSA | Ausa road | 4 |
| OSH | Old sachdeva halt | 0 |
| OSN | Osiyan | 8 |
| OSRA | Osra | 0 |
| OTD | Ootwar | 6 |
| OTK | Ottakovil | 6 |
| OTN | Oating | 2 |
| OTP | Ottappalam | 51 |
| OTR | Moturu | 13 |
| OV | Otivakkam | 6 |
| OVF | Ottivakkam | 0 |
| OYR | Waria | 40 |